Switching pattern AC induction motor

ABSTRACT

Both the stator core and the rotor core of a switching pattern AC induction motor are fabricated by soft magnetic material laminations or ferrite material, etc., both of which have corresponding frequency characteristic. The rotor is a squirrel cage rotor. Switching pattern excitation is adopted in the stator pole, of which the excitation voltage is sine wave pulse width modulated or sine wave pulse amplitude modulated within the frequency range of voice and ultrasonic. Under the condition of the same power output, the present motor reduces its size and mass to a fraction of or tenth of that of an ordinary one. Meanwhile, it reduces the cost of manufacture. It realizes stepless speed regulating from zero to several thousand rpm while keeping well mechanical characteristic performance.

TECHNICAL FIELD

The present invention relates to a novel motor, more particularly, to aswitching pattern AC induction motor within the frequency range of voiceand ultrasonic.

BACKGROUND ART

Existing AC induction motor, which is mainly squirrel cage type ACasynchronous induction motor, has the advantages of simple structure,low cost and larger output torque as compared with brush DC motor. Sucha motor is typically excited with continuous two phases of sine wavevoltages with a phase difference of 90° or three phases of sine wavevoltages with a phase difference of 120°. A continuous sine waverotating magnetic field is generated in the air gap between the statorand the rotor, which causes the squirrel cage type rotor rotating. Therotating speed of the motor can be approximately calculated by therotating speed formula for the rotating magnetic field: n=60*f1/p, wherep is the number of pole pairs of the stator in the motor, f1 is thefrequency of the excitation AC. It can be seen that, with the structureof the motor fixed, the rotating speed is mainly determined by thefrequency f1. Thus, an effective way to control the rotating speed is tovary the excitation AC frequency f1. For example, supposing the numberof pole pairs in the motor is p=2, the rotating speed per minute isn=1500 r/min when the excitation AC frequency f1=50 Hertz; the rotatingspeed is n=1200 r/min when f1=40 Hertz, and so on. For this reason, aplurality of methods of controlling the speed have been developed, suchas frequency-converting speed regulating and vector-controlling speedregulating, etc. However, since the actually required operating speed istypically much lower than the rotating speed of the motor, and becauseof the resistance characteristic of the excitation windings and thetorque requirement of the motor, such as the torque of the ACasynchronous motor is somewhat low during low-speed running, sometimes alower rotating speed can not be obtained by decreasing the excitation ACfrequency f1 without limitation. Therefore, it is often required to emexample, mechanical gears to vary speed, so as to meet variousrequirements in actual usage. In this way, the cost, size and weight ofthe apparatus are undoubtedly increased, and the effect is notsatisfying.

In the recent twenty to thirty years, permanent magnetic brushless DCmotor, step motor and switching reluctance motor, which can be generallyreferred to as electronic electromotor or electronic motor, are inventedand widely used. Mostly, their running principle is to rotate the rotorby alternatively using the attraction force or repulsion force generatedbetween the poles with the different polarity by control technology.This kind of motor has apparent improvement in aspects of speedregulating, the size and the weight, but the cost of manufacture, thespeed regulating range and the output torque still do not meet theincreasing requirements for higher performance.

SUMMARY OF THE INVENTION

The technical problems to be solved in the present invention are:

First, such a novel motor should have larger power density, that is tosay, under the condition of equivalent output power, the size and massof the motor is reduced to a fraction of or tenth of that of an existingone.

Second, such a novel motor has larger range of speed regulation ascompared with existing motors, the output speed thereof can becontinuously stepless adjusted between the rating rotating speed ofthousands of circles per minute and zero rotating speed, themanufacturing cost is cheaper, the size and mass is very small, and thespeed can be changed without gears while keeping constant torque.

The technical solution adopted to solve the above technical problems inthe present invention is:

Such a motor is achieved by adopting the AC electromagnetic inductiontechnique with switching frequency within the frequency range of voiceand ultrasonic, thus, it can be referred to as a voice frequency andultrasonic frequency switching pattern AC induction motor. Such a motoris composed of a machine base, a stator and a rotor, said statorincluding a core of cylinder shape, and stator teeth being disposed onthe internal surface of said stator core in equal angles and extendinginward along a radial direction with stator grooves penetrating along anaxial direction between the teeth; the number of the stator grooves orteeth being determined by the following equation: Z=2*M*P*Q, where Mbeing the number of phases of the excitation voltages, P being thenumber of pairs of stator poles, and Q being the number of grooves orteeth per pole per phase; excitation windings being disposed in thestator grooves, and the rotor of the motor being of a squirrel cagestructure; metal conducting bars of the ‘squirrel cage’ being disposedalong the axial direction and distributed at equal intervals in parallelwith a cylindrical surface of the rotor; characterized in that: saidexcitation windings on the stator of the motor being excited byswitching AC pulse pattern modulated excitation voltages, and the numberK of the metal conducting bars in the rotor ‘squirrel cage’ being twiceof the number P of pairs of the stator poles, i.e. K=2P. The excitationwindings on the stator are excited by switching AC pulse patternmodulated excitation teelmique, and the excitation voltage is a pulsemodulated voltage, which can be referred to as a sine wave pulsemodulated excitation voltage, generated after pulse width modulation orpulse amplitude modulation is performed on two phases of continuous sinewave voltages with phase difference of 9O° or three phases of continuoussine wave voltages with phase difference of 120°, which can be referredto as modulating sine wave voltages and have equal virtual values andfrequencies, together with a pulse square wave voltage within thefrequency range of voice or ultrasonic, which can be referred to as amodulating square wave voltage. When Q=1, the structure of theexcitation windings on the stator adopts centralized windings with 1/Mpole pitch or integral multiple pitch When Q>1, the distributed windingsare adopted. The cores of the stator and the rotor are made by softmagnetic material laminations which meet corresponding frequencycharacteristics within the frequency range of voice and ultrasonic, andsubject to surfiicc insulation treatment, then to piling along the axialdirection, and it can also be made of ferrite materials withcorresponding fiequency characteristic as a whole or in a manner ofsectioning along the axial direction.

The most essential innovation of the novel motor according to thepresent invention is the innovation of the excitation technique, i.e. itis excited by sine wave pulse modulated voltages within the frequencyrange of voice or ultrasonic, when the excitation windings in the statorare excited, the required pulsating alternating rotating magnetic fieldis generated in the air gap between the stator and the rotor, inducedcurrent is generated in the conducting bars on the rotor, and, thetorque of electromagnetic force in such a pulsating alternating rotatingmagnetic field is applied on the conducting bars, so that the rotor ofthe motor rotates. Supposing the frequency of the modulating sine wavevoltages is F1, the frequency of the modulating square wave voltage isF2, when the motor operates, the rotating speed of the pulsatingalternating rotating magnetic field only depends on the frequency F1 ofthe modulating sine wave voltages, and is independent of the frequencyF2 of the modulating square wave voltage, thereby the speed regulationof the motor can be achieved by changing the frequency F1 of themodulating sine wave voltages with a control circuit. Since the pulsefrequency of the sine wave pulse modulated excitation voltages, i.e. thepulsating alternating frequency of the rotating field, equals to thefrequency F2 of the modulating square wave voltage with its value withinthe frequency range of voice or ultrasonic, and is much larger than thefrequency F1 of the modulating sine wave voltages. It can be derivedfrom the basic principle of the electromagnet theory that, theresistance of the excitation windings of the motor is proportional tofrequency F2, and is independent of frequency F1 of the modulating sinewave voltages. The higher F2 is, the smaller the size and mass of thestator core, the rotor core and the windings of the motor are. As longas the frequency F2 is maintained to be relatively fixed, a stableoutput torque of the motor can be ensured even when the F1 approaches tozero frequency to obtain an extremely low rotating speed, thereby thecontinuous stepless speed regulation between the rating rotating speedof thousands of circles per minute and zero rotating speed can beachieved under good mechanism characteristic. Since the size of themotor is reduced, materials consumption can be greatly saved, and thestator core and the rotor core can adopt cheaper soft magneticmaterials, so the manufacture cost can be greatly reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a transverse sectional view of the stator and the rotor in atwo-phase motor with 16 grooves and 4 pairs of poles.

FIG. 2 is a schematic diagram of connection of the ½ pole pitchexcitation windings of the motor shown in FIG. 1 and the excitationvoltages.

FIG. 3 is a stretch-out view of the ½ pole pitch centralized excitationwindings in the motor shown in FIG. 2.

FIG. 4 is a schematic view of the waveforms of the sine wave pulsemodulated excitation voltages in the motor shown in FIG. 1.

FIGS. 5A, 5B are a view of the pulsating and rotating magnetic fieldgenerated by the excitation voltages shown in FIG. 4 and a schematicdiagram of the running of the rotor.

FIGS. 6A˜8B are stretch-out views of several kinds of integral multiplepitch excitation windings in the motor shown in FIG. 1.

FIG. 9 is a transverse sectional view of the stator and the rotor in athree-phase motor with 24 grooves and 4 pairs of poles.

FIG. 10 is a stretch-out view of the ⅓ pole pitch centralized excitationwindings in the motor shown in FIG. 9.

FIG. 11 is a schematic view of the waveforms of the sine wave pulsemodulated excitation voltages in the motor shown in FIG. 9.

FIGS. 12, 13 are views of the pulsating and rotating magnetic fieldgenerated by the excitation voltages shown in FIG. 11 and schematicdiagrams of the running of the rotor.

FIGS. 14A˜16B are stretch-out views of several kinds of centralizedexcitation windings in the motor shown in FIG. 9.

FIGS. 17, 18 are block diagrams of the excitation control circuits ofthe motor shown in FIG. 9.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a transverse sectional view of the stator and the rotor ina two-phase motor with 16 grooves and 4 pairs of poles, wherein “010” isa stator core with a shape of hollow cylinder, “101” are stator groovespenetrating along the axial direction, “102” is a stator yoke, “103” arestator teeth distributed in an identical angle and extending inwardalong the radial direction, the stator grooves and the stator teeth arearranged alternatively surrounding the internal surface, “020” is arotor having a cylindrical surface, “104” are conducting barsdistributed in parallel with equal intervals along the cylindricalsurface of the rotor core of the motor, the conducting bars and theconducting rings (not shown in the drawings) located at the twoend-faces of the cylinder are welded to be a metal inductor like asquirrel cage structure, “105” is a rotor core, “106” is a rotor shaft,“107” is the air gap between the rotor and the stator, the rotor shaftis supported by a rotor bearing (not shown in the drawings) on a machinebase connected with the stator core as a whole. When the number Z of thestator grooves or teeth is fixed, if the number of the stator grooves orteeth per pole per phase is Q=1, the number of pole-pairs and the numberof conducting bars corresponding thereto in the rotor can be increasedto obtain a larger output torque. In the embodiment shown in FIG. 1,since the number of phases of the excitation voltages is M=2, and thenumber of stator grooves [101] or teeth [103] is Z=16, when Q=1, thenumber of pole-pairs is P=Z/(2*M*Q)=4, there are 8 conducting bars inthe rotor, which is twice of the number of pole-pairs.

As described above, the excitation voltages concerned in the presentinvention are pulse excitation voltages generated by pulse widthmodulation or amplitude modulation on two phases of modulating sine wavevoltages with a phase difference of 90° or three phases of modulatingsine wave voltages with a phase difference of 120°, together with amodulating square wave voltage within the frequency range of voice orultrasonic. The modulating sine wave voltages can be referred to as Aphase, B phase and C phase modulating sine wave voltages respectively.For the convenience of explanation, the excitation voltage generated bypulse modulation on the A phase modulating sine wave voltage can bereferred to as A phase excitation voltage, the excitation voltagegenerated by pulse modulation on the B phase modulating sine wavevoltage can be referred to as B phase excitation voltage, and so on. Asshown in FIG. 4, Ur is a modulating square wave voltage having awaveform of symmetric square wave with a duty factor of 50%. Uas is theA phase modulating sine wave voltage, Ubs is the B phase modulating sinewave voltage, and Uas leads Ubs by 90°. Uwa, Uwb are respectively the A,B phase width modulated excitation voltages, and Uma, Umb arerespectively the A, B phase amplitude modulated excitation voltages. Aswell known, for a pulse width modulated excitation voltage, the pulseamplitude of the excitation voltage is fixed, and the pulse widththereof is proportional to the amplitude value sampled on the modulatingsine wave voltage at respective corresponding timings of modulatingsquare wave voltage. In the drawing, the lagging edge of each pulse inthe pulse width modulated excitation voltage is fixed at the rising edgeor falling edge of the modulating square wave voltage, and its leadingedge is variable. For a pulse amplitude modulated excitation voltage,its pulse width is fixed, and the pulse amplitude is proportional to theamplitude value sampled on the modulating sine wave voltage atrespective corresponding timings of the modulating square wave voltage.It can be seen from the drawing, the polarity orienting principle of thepulse amplitude of the pulse width modulated or pulse amplitudemodulated excitation voltages is: when the directions of the amplitudesof the modulating sine wave voltage and the modulating square wavevoltage are the same (i.e. both are positive or both are negative), apositive value is taken, which is a positive pulse; when the directionsof the amplitudes of the modulating sine wave voltage and the modulatingsquare wave voltage are the different (i.e. one is positive and theother is negative), a negative value is taken, which is a negativepulse. Further, the pulse amplitudes of the same phase excitationvoltage are always alternated positively and negatively along the timeaxis, except for the zero point of the modulating sine wave voltage.

FIG. 2 shows the centralized excitation winding with half pole pitch or½ pole pitch and the schematic diagram of its being connected with theexcitation voltages, the winding has separate excitation windings oneach stator tooth, thus it can be referred to as separate typeexcitation windings. For a centralized excitation winding with ½ polepitch, it is more convenient to describe with stator teeth. It can beseen from FIG. 2 that, as for 16 stator teeth thereof, in the order ofnumbers 1˜16, every two adjacent teeth constitute one pole, for example,the teeth 1, 2 constitute the first pole, the teeth 3, 4 constitute thesecond pole, the teeth 5, 6 constitute the third pole, and so on, thereare totally 8 poles. Every two adjacent poles are a pair of poles, forexample, the first and the second poles constitute the first pair ofpoles, the third and the fourth poles constitute the second pair ofpoles, and so on. There are totally 4 pairs of poles. Thus, each poleincludes two stator teeth and two stator grooves, thereby includes twoseparate excitation windings, and are switched in one phase of thetwo-phases of excitation voltages in a certain phase sequencerespectively. As shown in FIG. 2, for the odd teeth in each pole, suchas 1, 3, 5, 7 and so on, the excitation windings switch in the A phaseexcitation voltage; for the even teeth, such as 2, 4, 6, 8 and so on,the excitation windings switch in the B phase excitation voltage. Theleading-in terminals of the excitation voltages as shown in the drawingare terminals A1 and A2 respectively for the A phase excitation voltage,and are terminals B1 and B2 respectively for the B phase excitationvoltage. Further, it is stipulated that, when the excitation voltage ispositive pulse, the terminal “1” of respective phases of excitationvoltages, i.e. A1, B1 are the inflow terminals of the excitationcurrent, and are referred to as a head end; the terminal “2” thereof,i.e. A2, B2 are the outflow terminals of the excitation current, and arereferred to as a tail end. The manufacturing parameters of allexcitation windings are identical, and it is stipulated that, when theexcitation voltage is positive direction pulse, if the magnetometiveforce excited, on the end-face toward the rotor, by the stator teethwinded by the windings is N polarity, the excitation current is alwaysflowing in from the head end of the winding, and flowing out from thetail end of the winding, that is, the current inflow terminal of thewinding is referred to as the head end, and the current outflow terminalis referred to as the tail end. Thus, the connection relations betweenthe two excitation windings in each pole and the excitation voltagesshould be able to ensure that: when the two phases of excitationvoltages are both positive pulses, the pole is N polarity; when the twophases of excitation voltages are both negative pulses, the pole is Spolarity. The two poles in each pair of poles are antithetic poles ofeach other, the windings excited by the same phase excitation voltageand the stator teeth winded by them in the antithetic poles areantithetic windings and antithetic stator teeth of each other. Thewinding direction of the antithetic windings and the connectionrelations of them with the excitation voltages should be able to ensurethat, the polarities of the stator teeth excited by them are opposite toeach other, i.e. one is N polarity, and the other is S polarity.Typically, the antithetic windings in the same pair of poles, such asthe windings of teeth 1, 3 and the windings of teeth 2, 4 in the firstpair of poles, are connected in serial to be an antithetic branchcircuit in a manner of head to head or tail to tail. Then, the samenumbers of antithetic branch circuits are further connected in serial tobe a parallel branch circuit which is connected with the excitationvoltages. in parallel, so as to ensure that the resistances in everyparallel branch circuit are equal, for example, the number of theparallel branch circuits for every phase excitation voltage shown inFIG. 2 is α=4. FIG. 3 is a stretch-out view of the ½ pole pitchcentralized excitation windings corresponding to FIG. 2, in which theterminal with a dot “•” in each excitation winding represents the headend, and the terminal without dot represents the tail end, eachantithetic branch circuit acts as a parallel branch circuit. Thus, thenumber of parallel branch circuits for each phase is α=Z/2*M=4, whichare respectively represented by (1), (2), (3), and (4). If the terminalsA2, B2 in (1) are respectively connected with the terminals A1, B1 in(2), and the terminals A2, B2 in (3) are respectively connected with theterminals A1, B1 in (4), the number of parallel branch circuits for eachphase can be reduced to α=2; if the two parallel branch circuits areconnected with each other in serial in the same manner, the number ofparallel branch circuits can be reduced to α=1. As known from the basicelectromagnet theory, when the excitation winding is switched in thesine wave pulse width modulated or pulse amplitude modulated excitationvoltage, after the winding direction of the winding and the connectionrelations between the winding and the excitation voltage are determined,the direction of the excitation current generated in the winding isdetermined in accordance with the positive and/or negative polarity ofthe excitation pulse at each timing, and the amplitude of the current isrelated to the pulse width or pulse amplitude of the excitation voltage,and a corresponding magnetomotive force is generated across the statorteeth winded by the winding. Obviously, a larger excitation current canbe obtained by increasing the number of parallel branch circuits, so asto meet the requirement for larger output power of the motor.

In FIG. 5A, Fm represents the magnetomotive force generated by the pulsemodulated excitation voltage, wherein the maximum intensity of themagnetomotive force is roughly indicated by the number of magnetic linesof force, and the polarity of the magnetomotive force is indicated bythe arrow of the magnetic lines of force. In the drawing, according tothe connection manner between the excitation windings and the excitationvoltages, the polarity of the magnetomotive force excited by thepositive direction excitation pulse on the corresponding stator tooth isN, the magnetic lines of force direct from the stator tooth to therotor, and is represented by a downward arrow; the polarity of themagnetomotive force excited by the negative direction excitation pulseis S, the magnetic lines of force direct from the rotor to the statortooth, and is represented by an upward arrow. Since the excitationvoltage is a pulse alternating positively and negatively, the generatedmagnetic field is a pulsating magnetic field alternating positively andnegatively.

Hereinafter, the rotating status of the pulsating magnetic fieldalternating positively and negatively and the running principle of themotor will be explained with an example of the motor shown in FIG. 1,which is excited by the sine wave pulse modulated excitation voltagesshown in FIG. 4, in which the excitation windings and the excitationvoltages are connected in the manner shown in FIG. 2 and FIG. 3, withreference to FIGS. 5A and 5B. FIG. 5B comprises two parts on the leftand(on the right, in which the column (1) on the left is a sketch viewof the amplitudes and phases of the modulating sine wave voltages Uas,Ubs corresponding to FIG. 4, with the horizontal axis representing theamplitude of the modulating sine wave voltage and the vertical axisbeing the time axis; there are a plurality of sub-diagrams on the right,arranged along the vertical axis in two columns (2) and (3), eachsub-diagram has the same structure, and represents a part of thestretch-out view of the cross section of the stator and rotor in themotor shown in FIG. 1 being cut along a line A-A′ and further dissectedclockwise along the internal surface of the stator, with the sectionline on the internal surface of the stator as the horizontal axis, andits origin of coordinate being located at the intersection point of theline A–A′ and the internal surface of the stator, so as to show,corresponding to several specific timings shown in FIG. 4, thecorrespondence relations of the magnetomotive force generated by theexcitation windings and the running status of the rotor versus theamplitude values of the modulating sine wave voltages sampled at thetimings. Supposing, for the sampled value at each specific time, thereare positive and negative excitation pulses temporally close to eachother to correspond to it, and in the drawing, column (2) corresponds topositive direction pulses, and column (3) corresponds to negativedirection pulses. The temporal relation between the two parts on theleft and on the right in the drawing is indicated by dot lines.

Refer to FIG. 2 and FIG. 3, as described above, the excitation windingsof the odd teeth and the even teeth in each stator pole are respectivelyexcited by the A phase and B phase excitation voltages, for example,teeth 1, 3, 5, 7 etc. are excited by the A phase width modulatedexcitation voltage Uwa (or amplitude modulated excitation voltage Uma),teeth 2, 4, 6, 8 etc. are excited by the B phase width modulatedexcitation voltage Uwb (or amplitude modulated excitation voltage Umb).The letters A, B on the stator yoke are used to represent the excitationphase sequence for the corresponding stator teeth, the numbers drawn inbox “□” are used to represent the serial number of the stator teeth, themagnetic lines of force drawn on the section of the stator teeth areused to represent the strength and direction of the magnetomotive forcegenerated on the stator teeth at respective timings. Since the frequencyF2 of the modulating square wave voltage is much larger than thefrequency F1 of the modulating sine wave voltages Uas, Ubs, it can beregarded that the positive and negative excitation pulses temporallyclose to each other in the excitation voltages respectively have similarwidth (or amplitude), and the strength of the magnetomotive forcegenerated in the corresponding stator teeth should also be approximatelyidentical, with the directions being opposite.

Referring to column (1) and the first row of columns (2), (3) in FIG. 4and FIG. 5B, at the timing of t=00, since the A phase modulating sinevoltage Uas has a maximal value, the positive and negative pulses of theA phase excitation voltage Uwa corresponding to the timing have maximalpulse width value as well (the positive and negative pulses of Uwa havemaximal amplitude value as well); since the B phase modulated sine wavevoltage Ubs is 0, the pulse width of the B phase excitation voltage Uwb(or the amplitude of Uma) corresponding to this timing is 0 for bothpositive direction and negative direction. Therefore, the teeth number 1and number 3 excited by the A phase excitation voltage have the maximalstrength of magnetomotive force, which are represented by four magneticlines of force respectively. When the excitation voltage is a positivepulse, the magnetomotive force generated at the tooth number 1 is Npolarity, and the arrow of the magnetic line of force directs to therotor, the magnetomotive force generated at the tooth number 3 is Spolarity, and the arrow of the magnetic line of force directs to thestator yoke. The strength of the magnetomotive force generated at teethnumber 2 and 4 excited by the B phase excitation voltage is 0, so thenumber of its magnetic line of force is 0 as well. Supposing theposition of the rotor of the motor is just in the state as shown in thedrawing, that is to say, the conducting bars with serial number X1 andX2 on the rotor core are facing against exactly the middle of the statorteeth number 1, 3, then the close galvanic circuit formed by theconducting bars X1 and X2 together with the parts between the weldingpoints on the conducting rings of the two end-faces of the rotor can bereferred to as a X1-X2 induction circuit, which exactly faces againstthe stator segment centered on the middle of the tooth number 2. Thus,as shown in the cells in column (2), in the X1-X2 induction circuit, themagnetic flux flowed from the stator tooth number 1 into the rotorthrough the air gap is exactly equal to the magnetic flux flowed fromthe rotor core into the stator tooth number 3 through the air gap.Similarly, as shown in column (3), in the X1-X2 induction circuit, themagnetic flux flowed from the stator tooth number 3 into the rotor corethrough the air gap is exactly equal to the magnetic flux flowed fromthe rotor core into the stator tooth number I through the air gap. Thus,the variance ratio of the magnetic flux flowing in the X1-X2 inductioncircuit at the moment versus time is 0, so no induced current isgenerated in the close induction circuit, and no electromagnetic forceis applied on the conducting bars X1 and X2. As described above, becauseof the uniformity and symmetry of the structures of the rotor and statorin the motor, all of the other close induction circuits in the rotor arein the same status. Since all conducting bars in the rotor are notsubject to any torque of electromagnetic force, the rotor does notrotate.

However, during a period of changing from t=00 to t=04 via t=02, thething is different. In the cells in columns (2) and (3) of the secondrow in FIG. 5B, the strength and direction of the magnetomotive forcegenerated by the positive and negative excitation pulses correspondingto the timing t=02 in column (1) are shown. It can be seen that theamplitude of the A phase modulating sine wave voltage Uas is decreasedat t=02 as compared with that at t=00, the pulse width of the excitationvoltage Uwb (or the amplitude of Uma) corresponding to this is alsodecreased accordingly. Therefore, the magnetic lines of forcerepresenting the strength of the magnetomotive force of tooth number 1and tooth number 3 in the cells of column (2) is decreased from 4 to 3,in which tooth number 1 has arrows directing to the rotor and is Npolarity, tooth number 3 has arrows directing to the stator yoke and isS polarity. The amplitude of the B phase modulating sine wave voltageUbs is increased at t=02 as compared with that at t=00, the pulse widthof the excitation voltage Uwb (or the amplitude of Uma) corresponding tothis is also increased accordingly. Therefore, the magnetic lines offorce representing the strength of the magnetomotive force of toothnumber 2 and tooth number 4 in the cells of column (2) is increased from0 to 1, in which tooth number 2 has arrow directing to the rotor and isN polarity, tooth number 4 has arrow directing to the stator yoke and isS polarity. If the rotor of the motor and the X1-X2 close inductioncircuit thereof are still at the position of t=00, since the excitedmagnetomotive force or magnetic field on the respective stator teethcorresponding to it are changed, in the close induction circuit X1-X2,the magnetic flux flowing from stator teeth number 1, 2 into the rotorcore through the air gap is larger than the magnetic flux flowing fromthe rotor core into stator tooth number 3 through the air gap.Therefore, it can be known from the theory of electromagnetic inductionthat an induced current as shown in the drawing is generated in theX1-X2 close circuit, and its direction is as follows: the current in theconducting bar X1 facing against stator tooth number 1 flows outward,and the current in the conducting bar X2 facing against stator toothnumber 3 flows inward. Thus, both of the two conducting bars X1 and X2are subject to an electromagnetic force rightward, i.e. clockwise inrelation to the stator poles. Because of the uniformity and symmetry ofthe structures of the stator and rotor in the motor, the conducting barsin all of the other close inducting circuits in the rotor are subject tothe same electromagnetic force, thus the rotor will rotate clockwiseuntil a balance point of the torque is reached. At almost the same time,in the cells shown in column (3), supposing the width (or amplitude) ofits excitation pulse is scarcely changed, with only the direction beingreversed, i.e. changed from a positive pulse to a negative pulse, thenumber of the magnetic lines of force representing the strength of themagnetomotive force is not changed, but the direction of the magneticlines of force are reversed as compared with those of column (2). If therotor and its X1-X2 close induction circuit has reached a balance pointof the torque when the excitation voltage is a positive pulse,obviously, there is no induced current in the close induced circuit, andthe rotor does not rotate; if the X1-X2 close induction circuit has notreached a balance point of the torque when the excitation voltage is apositive pulse, an induced current opposite in direction with respect tocolumn (2) is generated in the X1-X2 close induction circuit. However,since the magnetomotive force or magnetic field corresponding to theconducting bars X1, X2 is also reversed, the electromagnetic forcecauses the circuit to move in the original direction, until a balancepoint is reached. The situation when time goes to t=04 is shown in cellsof column (2) and column (3) of the third row in FIG. 5B. According tothe same theory, the rotor also rotates clockwise with respect to thestator, until a new balance point of the torque is reached. So long asthe excitation phase sequence is not changed, such an alternatingpulsating rotating magnetic field, as well as the direction of thetorque of electromagnetic force generated in respective conducting barsof the rotor, will not change.

It can be seen from FIG. 5B that, when the time changes from t=00 tot=08 in the drawing, the modulating sine wave voltages in the excitationvoltages pass ¼ period, the conducting bars X1, X2 rotate along with therotor of the motor from the position facing respectively against thestator teeth number 1, 3 to the position facing respectively against thestator teeth number 2, 4, the number of teeth or grooves rotated byis 1. It can be concluded that, when the modulating sine wave voltagespass ½ period, the number of the teeth or grooves that the rotor of themotor rotates by is 2, i.e. a spatial angle of one pole pitch (shown asr in the drawing). When the modulating sine wave voltages pass 1 period,the rotor, of the motor rotates by exactly a spatial angle of one pairof poles, i.e. the rotor rotates by 1/P circle. Hence, the rotatingspeed per minute of such a motor .can be approximately calculated as:n=60*F1/P, which is the same as the above mentioned rotating speedformula of the conventional induction motor. However, for the motor,since the frequency F1 of its modulating sine wave voltages can approachto value of “0” without limit, its rotating speed can approach to zerowithout limit. It can be seen that the rotation of the rotor can bereversed by changing any phase of the two phases of excitation voltagesinto an excitation voltage reversed from the original excitation voltage(the reversed excitation voltage can be regarded as an excitationvoltage generated by modulating the modulating sine wave voltage of thisphase and the negative modulating square wave voltage).

Similar to the conventional induction motor, the manner constituting theexcitation windings of the present motor is not only like this one.FIGS. 6A–8B show the structures of several kinds of integral multiplepitch excitation windings in the motor shown in FIG. 1 with Q=1, whereinFIG. 6A shows a schematic view of A phase integral multiple pitch andsingle layer windings connected to be a parallel branch circuit, and theexcitation windings in the branch circuit are connected in serial withhead to tail or tail to head. FIG. 6B is a schematic diagram ofconnection of the A, B phases of integral multiple pitch and singlelayer windings, wherein the number of the parallel branch circuits isα=2, which are represented by (1) and (2) respectively. If the terminalsA2, B2 in (1) are respectively connected with the terminals A1, B1 in(2), the number of the parallel branch circuits of each phase can bereduced to α=1. The windings have simple structures with each statorgroove having only one coil side, which is adaptive for a motor withlower power. FIG. 7A is a schematic diagram of connection of theintegral multiple pitch windings in chain excited by the A phaseexcitation voltage, wherein each excitation winding is connected inserial with head to head or tail to tail, and constitutes a parallelbranch circuit, i.e. α=1. FIG. 7B is a schematic diagram of connectionof the integral multiple pitch windings in chain excited by both of Aand B phases of excitation voltages, with each stator groove having twocoil sides. In the drawing, the number of parallel branch circuits ofeach phase is α=4, which are represented by (1), (2), (3), (4)respectively. If the terminals A2, B2 in (1) are respectively connectedwith the terminals A1, B1 in (2), and the terminals A2, B2 in (3) arerespectively connected with the terminals A1, B1 in (4), the number ofthe parallel branch circuits of each phase can be reduced to α=2. In thesame manner, the number of the parallel branch circuits of each phasecan be reduced to α=1.

FIG. 8A shows a schematic diagram of connection of the integral multiplepitch wave windings excited by the A phase excitation voltage, in whichthe number of the parallel branch circuits is α=2. FIG. 8B shows aschematic diagram of connection of the integral multiple pitch wavewindings excited by both of A and B phases of excitation voltages, inwhich the number of the parallel branch circuits of each phase is stillα=2, if the excitation windings in phase are connected in serial in thedirection of the current, the number of the parallel branch circuits ofeach phase can be reduced to α=1.

Since the magnetic field excited by these integral multiple pitchexcitation windings are substantially the same as that excited by ½ polepitch windings, the previous analysis to the operational principle ofthe ½ pole pitch windings is also applicable. The present invention doesnot exclude excitation windings in other manner having equivalentfunctions as the excitation windings listed above.

FIG. 9 shows a transverse sectional view of the stator and the rotor ina three-phase switching induction motor with 24 grooves and 4 pairs ofpoles. In the drawing, “010” is a stator core, “101” are stator grooves,“102” is a stator yoke, “103” are stator teeth, “020” is a rotor havinga cylindrical surface, “104” are conducting bars, and the conductingbars and the conducting rings (not shown in the drawings) located at thetwo end-faces of the cylinder are welded to be a metal inductor like asquirrel cage structure. “105” is a rotor core, “106” is a rotor shaft,“107” is the air gap between the rotor and the stator, and the rotorshaft is supported by a rotor bearing (not shown) on a machine baseconnected with the stator core as a whole. It can be seen from thedrawing that, supposing Q=1, the number of phases of the excitationvoltages in the motor is M=3, and the number of stator grooves [101] orteeth [103] is Z=24, the number of pole-pairs is P=Z/(2*M*Q)=4, andthere are eight conducting bars in the rotor, which is twice of thenumber of pole-pairs.

The 24 stator teeth in FIG. 9 are grouped in the order of number 1˜24,every three adjacent teeth constitute one pole, for example, the teeth1, 2, 3 constitute the first pole, the teeth 4, 5, 6 constitute thesecond pole, the teeth 7, 8, 9 constitute the third pole, and so on,there are totally eight poles. Every two adjacent poles are a pair ofpoles, for example, the first and the second poles constitute the firstpair of poles, and the three and the fourth poles constitute the secondpair of poles, and so on, there are totally four pairs of poles. Sinceeach pole includes three stator teeth, three stator grooves and threeseparate windings, they are divided into three groups according to hespatial relative position in each pole. For example, the excitationwindings on teeth 1, 4, 7, 10, 13, 16, 19 and 22 are the first group,the excitation windings on teeth 2, 5, 8, 11, 14, 17, 20 and 23 are thesecond group, and the excitation windings on teeth 3, 6, 9, 12, 15, 18,21 and 24 are the third group, which switch into one phase of the threephases of excitation voltages respectively.

FIG. 11 is a schematic view of the waveforms of the three phases ofpulse excitation voltages in the motor shown in FIG. 9. In the drawing,Ur is the modulating square wave voltage, Uas, Ubs and Ucs are threephases of modulating sine wave voltages A, B, C, wherein Uas leads Ubsby an angle of 120°, Ubs leads Ucs by an angle of 120°, and Ucs leadsUas by an angle of 120°. It can be seen from the drawing that, thepolarity orienting principle of the pulse amplitude of the pulse widthmodulated (or amplitude) modulated excitation voltages is still asdescribed above, that is to say, a positive value is taken when thedirections of the amplitudes of the modulating sine wave voltages andthe modulating square wave voltage are the same, and a negative value istaken when the directions are different. Further, the pulse amplitudesof the same phase excitation voltage are always alternated in thepositive and negative directions along the time axis, except for thezero point of the modulating sine wave voltage.

FIG. 10 is a stretch-out view of the ⅓ pole pitch centralized excitationwindings in the motor shown in FIG. 9, the definitions and referencesigns of the leading-in terminal for the excitation voltages, the headends and the tail ends of the excitation windings are the same asmentioned above. In the drawing, the A phase excitation voltage Uwa (orUma) is switched into the excitation windings in the respective teeth inthe first group mentioned above, the C phase excitation voltage Uwc (orUmc) is switched into the excitation windings in the respective teeth inthe second group mentioned above, and the B phase excitation voltage Uwb(or Umb) is switched into the excitation windings in the respectiveteeth in the third group mentioned above. Such a phase sequence makesthe motor shown in FIG. 9 rotate clockwise, thus it can be referred toas clockwise excitation phase sequence. If the phase sequences of anytwo phases of excitation voltages are exchanged, for example, the threephases of pulse modulated excitation voltages shown in FIG. 11 arerespectively switched into the excitation windings in the respectiveteeth in the first, second, and third group mentioned above in a phasesequence of Uwa (or Uma), Uwb (or Umb), and Uwc (or Umc), the motorshown in FIG. 9 will rotate anticlockwise, thus it can be referred to asanticlockwise excitation phase sequence. In the drawing, all antitheticwindings are connected in serial to be an antithetic branch circuit in amanner of head to head or tail to tail, and each antithetic branchcircuit acts as a parallel branch circuit. Thus, the number of parallelbranch circuits of each phase is α=Z/2*M=4, which are represented by(1), (2), (3), (4) respectively. If the terminals A2, C1, B2 in (1) arerespectively connected with terminals A1, C2, B1 in (2), and theterminals A2, C1, B2 in (3) are respectively connected with terminalsA1, C2, B1 in (4), the number of the parallel branch circuits of eachphase can be reduced to α=2. If the two parallel branch circuits arefurther connected in serial in the same manner, the number of parallelbranch circuits of each phase can be reduced to α=1.

FIG. 12 schematically shows the pulsating rotating magnetic fieldgenerated when it is excited by the excitation voltages shown in FIG. 11in the above mentioned clockwise excitation phase sequence, as well asthe running of the motor. FIG. 12 also comprises two parts on the leftand on the right, in which the column (1) on the left is a schematicview of the amplitudes and phases of the A, B, C phases of themodulating sine wave voltages Uas, Ubs, Ucs shown in FIG. 12, with thehorizontal axis representing the amplitudes of the modulating sine wavevoltages, and the vertical axis being the time axis; there are aplurality of sub-diagrams on the right part column (2), arranged alongthe vertical axis in one column. Each sub-diagram has the samestructure, and represents a part of the stretch-out view of the crosssection of the stator and rotor in the motor shown in FIG. 9 being cutalong line A–A′ and further dissected clockwise along the internalsurface of the stator, with the section line on the internal surface ofthe stator as the horizontal axis, and its origin of coordinate beinglocated at the intersection point of the line A–A′ and the internalsurface of the stator, so as to schematically show, at several specifictimings shown in FIG. 11, the correspondence relation of themagnetomotive force generated at the stator teeth and the running statusof the rotor versus the sampled amplitude values of the modulating sinewave voltages at the timings. In order to simplify the analysis,supposing, for the sampled values at each specific time, there is onlyone positive or negative excitation pulse to correspond to it, whichappears alternatively in a time sequence as sampled. The temporalrelation between the two parts on the left and the right in the drawingis indicated by dot lines, and the definitions of the reference signsand expressions in the drawing is the same as those used above. It canbe seen from the drawing that, at time t=03, the conducting bars X1, X2are respectively located at the positions facing against the statorteeth number 3 and number 6; at t=21, the excitation voltages passexactly ½ period, and the conducting bars X1, X2 are rotated togetherwith the rotor to the positions respectively facing against the statorteeth number 6 and number 9, i.e. a spatial angle of one pole pitch(shown as r in the drawing) is rotated by. When the modulating sine wavevoltages pass 1 period, the rotor of the motor rotates by exactly aspatial angle of one pair of poles, i.e. the rotor rotates 1/P circle.Thus, for the three-phase motor shown in FIG. 9, the formula for therotating speed is the same as that of the above mentioned two-phasemotor. FIG. 13 schematically shows the pulsating rotating magnetic fieldgenerated when it is excited by the excitation voltages shown in FIG. 11in the above mentioned anticlockwise excitation phase sequence, as wellas the running of the motor. It can be seen from the drawing that, sincethe phase sequence of the excitation voltages is changed, the motorrotates reversely.

FIGS. 14A–16B show the structures of several kinds of integral multiplepitch excitation windings in the motor shown in FIG. 9 with Q=1, whereinFIG. 14A shows a schematic diagram of A phase integral multiple pitchand single layer windings connected to be one parallel branch circuit,and the excitation windings in the branch circuit are connected inserial in a manner of head to tail or tail to head. FIG. 14B is aschematic diagram of connection of the A, B, C phases of integralmultiple pitch and single layer windings, wherein the number of theparallel branch circuits is α=2, which are represented by (1) and (2)respectively. If the terminals A2, C1, B2 in (1) are respectivelyconnected with the terminals A1, C2, B1 in (2), the number of theparallel branch circuits of each phase can be reduced to α=1. Thewindings have simple structure with each stator groove having only onecoil side, which is adaptive for a motor with lower power. FIG. 15A is aschematic diagram of connection of the integral multiple pitch windingsin chain excited by the A phase excitation voltage, wherein eachexcitation winding is connected in serial in a manner of head to head ortail to tail, and constitutes one parallel branch circuit, i.e. α=1.FIG. 15B is a schematic diagram of connection of the integral multiplepitch windings in chain excited by three phases of excitation voltagesA, B, C, with each stator groove having two coil sides. In the drawing,the number of parallel branch circuits of each phase is α=4, which arerepresented by (1), (2), (3), (4) respectively. If the terminals A2, C1,B2 in (1) are respectively connected with the terminals A1, C2, B1 in(2), and the terminals A2, C1, B2 in (3) are respectively connected withthe terminals A1, C2, B1 in (4), the number of the parallel branchcircuits of each phase can be reduced to α=2. In the same manner, thenumber of the parallel branch circuits of each phase can be reduced toα=1. FIG. 16A is a schematic diagram of connection of the integralmultiple pitch wave windings excited by the A phase excitation voltage,the number of parallel branch circuits in the drawing is α=2. FIG. 16Bis a schematic diagram of connection of the integral multiple pitch wavewindings excited by three phases of excitation voltages A, B, C, thenumber of parallel branch circuits of each phase in the drawing is still2, if the excitation windings in phase are connected in serial in thedirection of the current, the number of the parallel branch circuits ofeach phase can be reduced to α=1.

FIG. 17 is a block diagram of the pulse width modulated excitationcontrol circuit of the motor with 24 grooves and 4 pairs of poles asshown in FIG. 9. In the drawing, the synchronous control pulse output bythe clock signal generating unit [11] is transmitted to the modulatingsquare wave generating unit [12] and frequency-converting sine wavevoltage generating unit [13] respectively. After subjecting tomicro-power pulse width modulation in pulse width modulating unit [14],the frequency convertible three phases of modulating sine wave voltagesUas, Ubs, Ucs with a 120° phase difference with respect to one anotherwhich are output by the frequency-converting sine wave voltagegenerating unit, and the modulating square wave voltage Ur output by themodulating square wave generating unit, are used to drive the powerswitching devices in the main switching unit [16] via A, C, B threephase driving unit [15]. The main switching unit has three groups of DChalf-bridge switching circuit made up of 6 power field effect switchingtransistors and 6 capacitors. Under the control of the driving circuit,two switching transistors in each DC half-bridge switching circuit turnon and off alternatively, so that three phases of pulse width modulatedexcitation voltages are output from A1, A2; C1, C2; B1, B2 respectively,so as to excite the stator windings. The power devices contained in thiscircuit is fewer, the circuit of the control part can be analogous ordigital, and can be integrated to dedicated circuits, and can bedeployed within the motor together with the power device, so as tofurther reduce its total size. High and low voltage DC power generatingunit [17] outputs DC high voltage required by the main switching circuitand DC low voltage required by the integrate circuit.

FIG. 18 is a block diagram of the pulse amplitude modulated excitationcontrol circuit of the three-phase motor with 24 grooves and 4 pairs ofpoles as shown in FIG. 7. It can be seen from the drawing that thecircuit is characterized in that: under the control of the synchronoussignal output by the clock signal generating unit [21], the driving unit25 is directly driven by the modulating square voltage output by themodulating square wave generating unit [22], the frequency-convertingcontrolling unit [23] synchronized by the clock signal generating unitcontrols the frequency-converting sine wave voltage generating unit [24]to output three phases of frequency convertible modulating sine wavevoltages Uas, Ubs, Ucs with sufficient power and amplitude. Themodulating sine wave voltage and the modulating square wave output bythe driving unit are subject to the amplitude modulation on power sinewave voltage in the main switching unit [26] by three groups of AChalf-bridge switching circuits made up of 12 power field effectswitching transistors and 6 capacitors, and then three phases ofamplitude modulated excitation voltages are output from its outputterminals A1, A2; C1, C2; B1, B2 respectively. The low voltage DC powergenerating unit [27] outputs DC low power to be used in the integratecircuit.

Obviously, the excitation control on pulse width modulation and pulseamplitude modulation in the two-phase motor with 16 grooves and 4 pairsof poles as shown in FIG. 1 can also be achieved in the same manner asdescribed above. The present invention does not exclude other controlcircuits having equivalent functions as described above.

1. A switching pattern AC induction motor comprising a machine base, astator and a rotor, said stator including a core of cylinder shape,stator teeth being disposed on the internal surface of said stator corein equal angles and extending inward along a radial direction withstator grooves penetrating along an axial direction between the teeth;the number of the stator grooves or teeth being determined by thefollowing equation: Z=2*M*P*Q, where M being the number of phases of theexcitation voltages, P being the number of pairs of stator poles, and Qbeing the number of grooves or teeth per pole per phase; excitationwindings being disposed in the stator grooves, and the rotor of themotor being of a squirrel cage structure, wherein: said excitationwindings on the stator of the motor being excited by a sine waveswitching AC pulse modulated excitation voltages, and the number K ofthe metal conducting bars in the rotor ‘squirrel cage’ being twice ofthe number P of pairs of the stator poles, i.e. K=2P wherein, the sinewave switching AC pulse modulated excitation voltages are generated byperforming pulse width modulation or pulse amplitude modulation on twophases of continuous modulating sine wave voltages with phase differenceof 90° or three phases of continuous modulating sine wave voltages withphase difference of 120° with equal virtual values and frequencies,together with a pulse square wave voltage having a waveform of symmetricsquare wave with a duty factor of 50% of which the frequency (F2) iswithin the frequency range of voice or ultrasonic and much larger thanthe frequency (F1) of said continuous modulating sine wave voltages. 2.The motor according to claim 1, characterized in that,wherein metalconducting bars of the ‘squirrel cage’ being disposed along the axialdirection and distributed at equal intervals in parallel with acylindrical surface of the rotor.
 3. The motor according to claim 1,wherein when the number of grooves or teeth per pole per phase is Q=1,the excitation windings on the stator adopt centralized windings with1/M pole pitch or integral multiple pitch.
 4. The motor according toclaim 1, wherein when the number of grooves or teeth per pole per phaseis Q>1, the excitation windings on the stator adopt distributedwindings.
 5. The motor according to claim 1, wherein the frequency (F1)of the continuous modulating sine wave voltages determines the rotationspeed of the motor, and can be changed to perform speed control of themotor.
 6. The motor according to claim 1, wherein the resistance of theexcitation windings of the motor is proportional to the frequency (F2)of the pulse square wave voltage, and the higher F2 is, the smaller thesize and mass of the stator core, the rotor core and the windings of themotor are.
 7. The motor according to claim 1, wherein cores of the rotorand the stator are made by soft magnetic material laminations which meetcorresponding frequency characteristics (F2) within the frequency rangeof the pulse square wave voltage, and subject to surface insulationtreatment, then to piling along the axial direction, or made of ferritematerials with corresponding frequency characteristic as a whole or in amanner of sectioning along the axial direction.